JAJSNP4A May 2023 – February 2024 TPS54KB20
PRODUCTION DATA
To determine the proper ramp selection for this design, the L-C double pole frequency and the maximum L-C double pole frequency must be calculated. The double pole frequency is based on the selected output inductance and output capacitance for this design. Using Equation 30, the L-C double pole frequency for this design is 10kHz. Calculating the maximum L-C double pole frequency then helps guide the user to select one of the four ramp options. Generally, if the L-C double pole calculation lands within the RAMP1 margin, select RAMP1, as this results in the best transient response. Select RAMP2 or RAMP3 if the L-C double pole calculation does not fit within the RAMP1 margin. TI recommends RAMP2 for an increase in phase margin, while TI recommends RAMP3 for higher gain and a faster transient response than RAMP2. If RAMP1, RAMP2, or RAMP3 cannot be selected due to maximum L-C double pole frequency restriction, then choose RAMP4. The maximum L-C double pole frequency can be calculated using Equation 31, where the variable fP(TABLE) equates to the RAMP1 maximum L-C double pole from Table 6-2. This calculation results in 15kHz, 19.7kHz, and 21.8kHz, for RAMP1, RAMP3, and RAMP4 respectively. Because the L-C double pole frequency in this design is 10kHz, which is less than RAMP1, RAMP1 is selected.
After selecting RAMP1 for this design, connect the MSEL pin to AGND using a 86.6kΩ resistor to set the switching frequency to 800kHz and the ramp option to RAMP1.